At the present stage of circuit production, integrated circuit chips are manufactured by a photographic reduction process that includes the deposition and etching of extremely thin conductive and semi-conductor materials in a plurality of microscopic patterns on a thin wafer or disc of silicon. Such silicon wafers are generally formed with standard diameters of three, four or five inches and each may contain several hundred individual and identical printed or integrated circuits to be cut apart, bonded and sealted in the final packages.
It is a standard quality control step to inspect each of the many microscopic circuits deposited on each silicon wafer prior to the cutting and packaging of the chips. The normal process for such inspection is to manually position a printed silicon wafer on the adjustable XY stage of an inspection microscope and, after the inspector has completed the examination of each individual circuit and has marked all that were defective, the wafer is manually returned to the disc holder for further processing, including the cutting, packaging and final electronic testing.
Unfortunately, there are substantial losses to both individual circuits and the entire circuit wafer caused by a manual handling of the wafer in the optical inspection step. After the silicon discs or wafers are printed with the large quantity of individual circuits, they are loaded into conventional disc holders which normally carry a stack of approximately twenty-five wafers separated and supported at their edges. Each disc carrier is moved to an optical inspection station where an inspector manually removes one wafer at a time for its microscopic examination and then manually transfers the inspected wafer back to the disc carrier.
Prior to their final packaging, the microscopic circuits are extremely vulnerable to contamination and the large, very thin silicon wafers are easily fractured or broken if mishandled. The microscopic inspection site may be located in a dustproof clean room and the inspection personnel may be properly masked and gloved to minimize the dangers of contamination. However, gloves greatly increase the possibility of mishandling a wafer and many wafers, each carrying a great many individual circuits, are scratched, dropped, contaminated, or broken in the process of moving them from the disc holders to the microscope stage and then from the stage back into the disc holders.
The present invention is for a transfer mechanism which transfers the wafers between the disc holder and the field of view of the inspection microscope and subsequently back to the disc holder without any manual contact with the wafer, thereby substantially eliminating the possibility of contamination, fracturing, dropping or breaking during the optical inspection process.